Mobile radio network operators currently have the option of operating not only the prevalent mobile radio systems using the GSM standard, but also networks using the new UMTS standard. Established network operators often currently set up a UMTS network, in parallel to an existing GSM network, which is characterized by the provision of expanded functionalities such as multimedia connections and higher packet data rates. At the present time, network operators operating on GSM as well as UMTS networks typically operate their networks in such a way that so-called dual-mode mobile telephones, that is, mobile telephones, which support both GSM and UMTS networks, preferably “camp” on the UMTS network. In this context, “camping” refers to the state of the mobile telephone in which no active connection exists between the mobile telephone and the mobile radio network, but the mobile telephone is logged onto the UMTS network (see Specification 3GPP TS25.3•04). If such a “camped” mobile telephone then attempts to establish a voice connection, for example, with the mobile radio network, using the UMTS standard the mobile telephone sends an RRC CONNECTION REQUEST message to the mobile radio network, as may be learned from technical specification ETST TS125.331, V7.0.0; Universal Mobile Telecommunications System (UMTS); Radio Resource Control (RRC) Protocol Specification; March 2006: (see 3GPP TS 25.331, Version 7.0.0, Release 7). According to the prior art, the mobile radio network then establishes the desired voice connection in the UMTS network and sets up the connection with the called party and the calling subscriber. A voice connection thus occupies resources of the UMTS network. Alternatively, this connection could be implemented on the GSM portion of the mobile radio network, since this portion is able to meet the technical requirements for serving the needs of a simple voice connection.
In such mobile radio networks, to avoid unnecessary occupation of resources by simple voice connections as the result of the preferential camping of all dual-mode mobile telephones on the UMTS network, and with increasing prevalence of UMTS- and GSM-capable devices, to prevent “idling” of the established GSM networks due to the preferred camp strategy of dual-mode mobile telephones on the UMTS portion of the mobile radio network, appropriate measures are necessary to make further use of the free resources of the GSM portion of a mobile radio network.
In the prior art, mobile radio operators are currently able to use technologies which, in a given phase of establishing a connection or using an existing connection, “redirect” the voice connection from the UMTS portion of the mobile radio network to the GSM portions of the same mobile radio network in order to once again utilize, as needed, unused resources on the GSM network. These technologies are often referred to as “service-based handover” or “directed retry” in the specifications for the mobile radio network (www.3gpp.org).
The primary disadvantage of the prior art is that the decision to carry out the service-based handover or directed retry can be made only in a very late phase of establishing a connection, namely, only at the time at which, for the mobile radio network for example, the radio network controller (RNC) for UMTS, the particular reason for starting the establishment of a connection, is known. Although the mobile telephone, using the UMTS standard according to (3GPP TS25.331), communicates information concerning the reason for establishing the connection to the network in the RRC CONNECTION REQUEST or CELL UDPATE message, the currently available “establishment causes” do not allow an unambiguous conclusion to be drawn concerning the particular service for which the connection is to be established. The reason for the channel request, for example, voice transmission, data transmission, among others, is specified in the information element establishment cause. Using the currently available establishment causes it is not possible in particular to unambiguously determine whether a circuit-switched (CS) voice connection, a simple voice service (possible via UMTS and GSM), a voice connection using the wideband AMR codec, or a video telephone conversation (only possible in UMTS) is requested by the mobile telephone for the connection establishment request. This information is not available to the radio network control (RNC) as a control function for the radio access network until the time that an RRC connection has been established between the mobile radio device and the radio network control unit and further signaling in the direction of the core network (CN) has been carried out via the Iu interface (3GPP TS 25.413). According to the prior art, the earliest point in time of the decision as to whether a voice or video service is to be established is the arrival of the RANAP: RAP ASSIGNMENT message.
WIPO patent application publication, WO 2005/101880 A1, discloses a method for optimizing the load distribution between a first mobile radio network, for example, using the UMTS standard, and a second mobile radio network, for example, using the GSM standard, in which accurate information concerning the type of connection request is provided to a radio network control unit for a radio access network in the earliest possible phase of establishing a connection with a mobile radio device. On the basis of this information a resource allocation between the two mobile radio networks is made before the radio access network (RAN) has established a connection with a core network of one of the mobile radio networks.